The present invention relates to a novel dielectric ceramic material which shows a high relative dielectric constant and a high Q factor in high frequency regions such as microwaves and millimeter waves and, more particularly, to a dielectric ceramic material suitable for forming high frequency electronic components such as dielectric resonator, filter and capacitor, dielectric substrate for MIC and waveguide for millimeter-wave applications.
Dielectric ceramic materials have been widely used in dielectric resonators and dielectric substrate for MIC which are used in high frequency applications such as microwave and millimeter waves. Recently dielectric strip line has found applications in millimeter band waveguides. The major requirements for the dielectric ceramic material are as follows.
(1) The material must have high relative dielectric constant when used to make a small-sized component, since the electromagnetic wave propagating in a dielectric material has a wavelength reduced to (1/∈r)1/2.
(2) The material must have less dielectric loss, namely a high Q factor, at high frequencies.
(3) Resonant frequency of the material must be subject to less variation when the temperature changes, that is, the relative dielectric constant ∈r must be stable with less temperature dependency.
The present applicant previously proposed, as the materials that satisfy these requirements, a BaMgW-based dielectric ceramic composition consisting of BaO, MgO and WO3 in a particular composition range (Japanese Unexamined Patent Publication No. 5-205524), a SrMgW-based dielectric ceramic composition consisting of SrO, MgO and WO3 in a particular composition range (Japanese Unexamined Patent Publication No. 6-5117), and a (BaMgW +3a group element of periodic table)based dielectric ceramic composition consisting of BaO, MgO, WO3 and an oxide of 3a group element in a particular composition range (Japanese Unexamined Patent Publication No. 6-236708).
There has been such a problem that, the BaMgW-based dielectric ceramic composition (Japanese Unexamined Patent Publication No. 5-205524), the SrMgW-based dielectric ceramic composition (Japanese Unexamined Patent Publication No. 6-5117), and the (BaMgW+3a group element)-based dielectric ceramic composition (Japanese Unexamined Patent Publication No. 6-236708) have Q factors ranging from 25000 to 180000, which are converted to values on the basis of 1 GHz, in a range of relative dielectric constant ∈r from 19 to 25. As the Q factor can become less than 100000, it has been required to improve the Q factor.
A main object of the present invention is to provide a dielectric ceramic material which has Q factor not less than 100000 in a range of relative dielectric constant ∈r from 19 to 25, particularly a dielectric ceramic material which has a high value of Q factor not less than 130000 in a range of relative dielectric constant ∈r from 19 to 25, and a dielectric resonator based on the same.
Another object of the present invention is to provide a dielectric ceramic material having relative dielectric constant ∈r which is less dependent on the temperature, namely that is stable with smaller absolute value of temperature factor xcfx84f of resonant frequency, and a dielectric resonator based on the same.
The dielectric ceramic material of the present invention which achieves the objects described above is a solid solution of which dominant crystal phase is a perovskite crystal, and the perovskite crystal comprises a complex oxide of at least Ba, Sr, Mg, W and RE (RE represents rare earth element).
The dielectric ceramic material of the present invention preferably contains the perovskite crystal comprising a complex oxide of at least Ba, Sr, Mg, W and RE, in a proportion of at least 90% by volume.
The dielectric ceramic material of the present invention preferably contains at least Ba, Sr, Mg, W and a rare earth element as metal elements, and when oxides of the metal elements are represented by aBaOxc2x7bSrOxc2x7cMgOxc2x7dWO3xc2x7eRE2Ox (3xe2x89xa6xc3x97xe2x89xa64, RE represents a rare earth element)) in a molar ratio of the metal oxides, the factors a, b, c, d and e satisfy the following relationships:
0.35xe2x89xa6axe2x89xa60.55,
0.01xe2x89xa6bxe2x89xa60.25,
0.10xe2x89xa6cxe2x89xa60.30,
0.15xe2x89xa6dxe2x89xa60.35,
0.01xe2x89xa6exe2x89xa60.20, and
a+b+c+d+e=1
RE of the dielectric ceramic material of the present invention is preferably Yb. It is also preferable that the dielectric ceramic material of the present invention contains Mn as the metal element in the amount of 0.01 to 2% by weight on MnO2 basis.
The dielectric resonator of the present invention is made in such a constitution as the dielectric ceramic material described above is disposed between a pair of input and output terminals so as to function through electromagnetic coupling.
Other objects and advantages of the present invention will become apparent from the following detailed description.